This invention relates to machines for laying a web to form superpositioned web layers. By "web" there is meant a flexible sheet material which may be a fabric or other woven or non-woven material and which, as stock material, has a predetermined width and generally an indetermined length.
Web laying machines generally have an elongated laying table on which a laying carriage, propelled by a drive supported thereon, travels back and forth. The end positions (that is, the locations where the direction of travel of the laying carriage is reversed) are determined by means of limit switch assemblies which are adjustable in the longitudinal direction of the laying table. Conventionally, the laying carriage supports the web stock wound on a core and further, the laying carriage has a pulling device which can be connected to or disconnected from a drive by means of a switchable clutch. The pulling device comprises take-off rolls for pulling the web from the supply. Extending from the supply, the web passes through a web deflecting device (hereafter web laying unit) which is supported on the laying carriage and which is displaceable vertically with respect thereto. The web laying unit deflects the web approximately into a horizontal direction and deposits it on the laying table.
There are further known laying machines wherein the web stock is stored in a zigzag-folded stack and it is further feasible to arrange the supply stationarily apart from the laying carriage.
By means of the known web laying machines a web can be laid according to a number of processes. The simplest process is the so-called simple laying mode. In such a method, at one terminal position of the laying carriage there is provided a web holding unit for immobilizing the web lengths to be laid. The web holding unit usually comprises a web grasping rail. During the course of the laying operation, the laying carriage first travels up to the web grasping rail, then raises the same during approach in such a manner that the web grasping rail, upon reversal of the traveling direction of the laying carriage, comes to rest on that portion of the web which has just left the web laying unit and then the web grasping rail pulls the web onto the laying table and immobilizes it thereon, whereupon the laying carriage, during its travel towards its second, opposite terminal position, deposits a web layer onto the laying table. As the laying carriage stops in its second terminal position, a cutting device which is movable transversely to the laying table along the web laying unit, severs the deposited web layer from the web supply. Thereupon the laying carriage, without performing a laying operation, travels to the first terminal position, thus completing a cycle of the repetitive operation.
In the so-called zigzag laying mode, the laying carriage deposits web lengths on the laying table during travel in both directions. For this mode the laying machine has a web holding unit also at the location of the second terminal position of the laying carriage.
The known web laying machines and laying methods have a number of disadvantages. Thus, since particularly textile webs have the tendency to bulge along the edges of the web laid out on the laying table (in case of some materials the edge regions may bulge as much as 30 mm beyond the height of the web stack), the laying carriages of the known web laying machines move the web laying unit at a substantial height back and forth above the uppermost web layer. Consequently, as the laying carriage leaves the respective terminal position, the web grasping rail (or rails, as the case may be) pulls the web over a substantial vertical length onto the laying table or, as the case may be, onto the uppermost web layer. This, in turn, means that the deposited web is either not free from longitudinal stresses and therefore is not distortion free or the web pulling device of the laying carriage has to operate with a material excess, that is, it has to draw off more material from the supply than what would correspond to the path traveled by the laying carriage. Such an operation would again be inconsistent with the requirement for a planar and uniformly laid web layer.